Page 387 - Tandem Techniques

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ratio it would seem that the assay could detect levels of Cloxacillin as low as 40 ng/g.

Figure 9.30
Chromatogram from the Assay of Cloxacillin and
Penicillin G Monitored at Different m/z Values (ref. 25)

The optimum extraction voltage for assaying Penicillin G in milk appears to be far more critical, the
best selectivity being obtained at a m/z value of 333. The lower limit of detection, however, is much
smaller and it looks as if less than 1 ng/g might be detectable.

Research by Elliot et al. [26], involving the correlation of stereochemical structure with insecticidal
activity led to the discovery of permethrin, cypermathrin and many other important pyrethroids. The
new pyrethroids lack the cyclopropanecarboxylic ester bond, common to other chemically similar
insecticides, and are mainly achiral. They are broadly insecticidal, have low mammalian toxicity's, and
as a result are applied to crops, forests, soils, animal feeds and in household use. It follows, that an
assay, capable of detecting very low concentrations of such substances is necessary for environmental
testing. Fleet et al. [27] developed such a technique using positive-ion electrospray mass spectrometry.
A VG tandem quadrupole mass spectrometer fitted with an electrospray